Forget spiders, scientists turn silkworm thread into nature’s most powerful material

TIANJIN, China — Silkworm thread has been turned into the world’s most powerful natural material, according to new research. Scientists in China say they’ve made it 70 percent stronger than a spider’s silk by removing a sticky outer layer and spinning it manually.

Thinner than a human hair, silk is lighter than cotton, but five times harder than steel — relative to its weight. It is capable of holding objects hundreds of times its size and is woven into elaborate structures to help humanity.

Spiders hold the market for producing the best silks, but they’re too aggressive and territorial to use in silk farms. The next best alternative involves incorporating their DNA into silkworms, an expensive and difficult-to-scale process. The new study provides an innovative alternative.

“Our finding reverses the previous perception that silkworm silk cannot compete with spider silks on mechanical performance,” says senior author Zhi Lin, a biochemist at Tianjin University, in a media release.

The breakthrough, described in the journal Matter, could be a gamechanger for a range of industries, including the construction and medicine fields.

Historically, silk symbolizes wealth and status. People have used it in the creation of luxury robes and apparel fitting for royalty. Today, it is a more common fabric in biomedicine, used for stitches and surgical mesh, or for tissue regeneration due to its biocompatibility and biodegradability.

Farmed silkworms are the most common source, but these silks are weaker and less durable than spider draglines which naturally do well under high tension.

“Dragline silk is the main structural silk of a spider web. It is also used as a lifeline for a spider to fall from trees,” says Lin.

Stress-strain curves of representative artificial and natural silks. (CREDIT: Jingxia Wang, Tiantian Fan, & Zhi Lin)

How did scientists alter worm silk?

Silkworms use their softer silks for the construction of cotton ball-like cocoons during transformation into moth forms. Dr. Lin and colleagues were inspired by the artificial spinning of spider eggcase silk, a close relative to silkworm silk which does well in the spinning process.

Natural silkworm silk is composed of a core fiber wrapped by glue. It interferes with spinning for commercial purposes. So, the researchers boiled silk from the common silkworm Bombyx mori in a bath of chemicals that could dissolve the glue and minimize degradation of proteins. Solidifying it in a bath of metals and sugars enhanced the spinning.

“Since silkworm silk is very structurally similar to eggcase spider silk, which has previously been demonstrated to do well in a mix of zinc and iron baths, we thought to test this alternative method to avoid hazardous conditions used elsewhere,” Lin explains. “Sucrose, a form of sugar, may increase the density and viscosity of the coagulation bath, which consequently affects the formation of the fibers.”

Once manually spun and drawn, the silks are thinner than the original silkworm silk, reaching nearly the same size as spider silks. Scanning them under a microscope showed they were “smooth and strong,” indicating the artificial fibers could withstand force.

“We hope that this work opens up a promising way to produce profitable high-performance artificial silks,” Lin says.

Natural silk has existed for more than 300 million years

Mimicking the silk that silkworms and spiders create is big business. It is produced by animals belonging to the phylum Arthropoda. Silkworms, spiders, lacewings are among the creatures that can produce the incredible natural substance.

Silk is beautiful, but outside of the aesthetic value and the ability to create garments, the property most people are interested in is its strength. The fibers are some of the strongest in nature and are well tolerated when implanted in sheep, rats, and pigs. This means they have promising applications in medicine.

Spider and silkworm silks are made using unique proteins which are spun in the creature’s glands. Silkworms are the larva, or caterpillar, of the Bombyx silk moth and can be used for silk textile production as they are easily farmed in great numbers.

The silkworm pupates in a protective cocoon which it spins from silk secreted from its salivary glands. The cocoon’s silk is colorless, and it is easily cleared of minerals, making them an ideal material for winding into a thread. In contrast, spiders use their silk for web building, reproduction, and catching prey, although they produce comparatively small amounts.

South West News Service writer Mark Waghorn contributed to this report.

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